The need for mobile electrical power generation systems has traditionally been satisfied with generators powered by internal combustion engines fueled with material such as gasoline or diesel fuel. While these systems have proven reliable and efficient in numerous applications, they are not suitable in certain other applications. For example, in many military applications the requirement that a single fuel source power both a vehicle and an auxiliary power system prevents the use of off-the-shelf internal combustion gasoline generator systems. Additionally, issues related to the noise and vibration generated by internal combustion systems can render their use unacceptable in particular situations.
One alternative to typical internal combustion systems are fuel cell-based electrical power generation systems. Of particular interest are polymer electrolyte membrane (PEM) fuel cells used in conjunction with steam reforming systems. Combining a PEM fuel cell with a steam reforming system, these systems provide a mobile source of electricity that is quiet, efficient, and capable of being powered by a variety of hydrocarbon fuel streams.
Generally speaking, fuel cells generate water and electricity as outputs. In addition, combustion processes such as those used to heat a steam reformer generate water vapor. However, steam reforming systems use water as an input. Therefore, power generation systems that combine fuel cells with steam reforming systems must have water available as an input, or make efficient use of water formed in the fuel cell and reformer combustor. Operation of these power generation systems in environments with high temperatures requires efficient use and recovery of water. Maintaining a positive water balance, where water condensed and recovered exceeds that being fed to the process, becomes more and more difficult for high ambient temperatures (i.e. >40° C.) due to the close approach temperatures that must be achieved in the radiator and condenser. The result is that a system designed to reach water balance at high ambient temperature will have very large radiators and have a significant parasitic penalty for radiator fan power. At some point, maintaining positive water balance is simply not possible regardless of radiator size.
Accordingly, there exists a need for methods and apparatus that allow a power unit for generating electrical power that has a steam reforming system and a fuel cell to conserve water available to the power unit. There is a further need to increase the efficiency of a power unit for generating electrical power that has a steam reforming system and a fuel cell.